1. Field of the Invention
The present invention relates to a data communication apparatus which performs communications with other apparatuses with two methods including a method of transferring data from a single transfer source to another single transfer destination and a method of transferring data from a single transfer source to a plurality of other transfer destinations concurrently. Especially the present invention relates to a data communication apparatus which has a communication part which employs an IEEE (Institute of Electrical and Electronic Engineers) 1394 interface, a USB (Universal Serial Bus) interface, or so. Moreover, the present invention relates to a data communication system including the data communication apparatus and other apparatuses which act as data transfer destinations, a data communication method used in the data communication apparatus for performing the data communications, a data communication program which causes a computer which acts as a data communication apparatus to execute the data communication method, and a computer-readable information recording medium in which the data communication program is recorded.
2. The Description of the Related Art
In recent years, in order to transfer data which needs to be transferred in a real-time manner such as an animation or a sound, a telecommunication standard which has a mode (which guarantees transmission of data via a predetermined frequency band within a predetermined interval) called an isochronous transmission mode, has been enacted. This is for example, an IEEE Std 1394 standard or a USB standard, and communication interfaces based on the standards have been used widely.
Generally, such isochronous transmission achieves a high throughput compared with a so-called asynchronous transmission which performs reception check of data, and thus is suitable for a use of transferring within a predetermined time a lot of data. Therefore, it is possible to apply this mode also for transmission of image data for a printing apparatus, a scanner, or so other than transmission of so-called multimedia data, such as an animation, a sound, or so.
However, in the above-mentioned isochronous transmission mode, reception check of data is not performed instead of band width being guaranteed. Therefore, even if lack of data occurs due to a certain cause, re-transfer or so is not performed. Such a matter hardly becomes a problem in a use of transmission of an animation or a sound. However, for such a type of data as still image data used for a printing use, software program data or so for which even exiguity error cannot be allowed, it may cause a fatal problem. By this reason, a certain countermeasure is required.
Japanese laid-open patent application No. 10-111773 discloses a scheme for solving this problem. This enables bidirectional communications between a printer and a printer controller by carrying time sharing on a single isochronous channel. According to this configuration, data can be broadcast again even when an error occurs.
Japanese laid-open patent application No. 10-307691 discloses a scheme that printing data is transferred to a printing apparatus from a host by isochronous transmission, and, when an error occurs, it is notified to the host and the data is made to be re-transferred by asynchronous transmission.
Japanese laid-open patent application No. 10-164174 discloses a scheme that isochronous transmission is applied to perform data transmission, and, when an error occurs, asynchronous transmission is applied to make a resending request. Then, according to this, data is transferred by isochronous transmission.
According to such technologies, isochronous transmission can achieve high-speed data transmission. Furthermore, even when an error occurs, a recovery is performed, and, thus, reliable data transmission can be performed.
By the way, in the isochronous transmission, a so-called multicast method of transferring data to a plurality of transfer destinations concurrently from a single transfer source is applicable. That is, data transmission in a broadcast manner is attained. According to this method, printing data may be transferred simultaneously to a plurality of printers from a PC (personal computer), and, thus, simultaneously, each printer may be made to print the data, for example.
Japanese laid-open patent application No. 2000-49834 discloses a scheme of controlling data transmission in such a case, for example. This scheme chooses from a plurality of communication protocols a communication protocol used between a source node and a destination node. These plurality of protocols from which a relevant one is selected includes one of multicast method (for example, of isochronous transmission), and a unicast method (for example, of asynchronous transmission) of performing communications in a one-to-one manner.